Vehicle safety device

ABSTRACT

A vehicle safety device installed in a hybrid electric vehicle or an electric vehicle is provided to be capable of interrupting a current supplied from a power supply to a load via a supply line. The vehicle safety device includes first interrupting mechanism adapted to set the supply line in an interrupted condition when a temperature of the load reaches a first set temperature and second interrupting mechanism adapted to set the supply line in the interrupted condition such that the supply line cannot be returned to an energized condition when the temperature of the load reaches a second set temperature that is higher than the first set temperature.

FIELD OF THE INVENTION

This invention relates to a vehicle safety device that interrupts acurrent when an abnormality occurs.

BACKGROUND OF THE INVENTION

JP10-145205A discloses a switch circuit that interrupts a currentsupplied to a load when a temperature detected by temperature detectingmeans reaches or exceeds a predetermined temperature. In this switchcircuit, control means open a switch on the basis of a signal from thetemperature detecting means, thereby interrupting input of a controlsignal into a MOSFET (Metal-Oxide-Semiconductor Field-EffectTransistor), and as a result, the current supplied to the load isinterrupted.

SUMMARY OF THE INVENTION

In the switch circuit of JP10-145205A, however, the current supplied tothe load is interrupted by having the control means open the switch onthe basis of the signal from the temperature detecting means, andtherefore, when an abnormality of some kind occurs in the control meansafter the current has been interrupted, supply of the current to theload may be resumed.

This invention has been designed in consideration of the problemdescribed above, and an object thereof is to improve the reliability ofcurrent interruption when an abnormality occurs in a load.

According to embodiments of this invention, a vehicle safety deviceinstalled in a hybrid electric vehicle or an electric vehicle isprovided to be capable of interrupting a current supplied from a powersupply to a load via a supply line. The vehicle safety device includesfirst interrupting mechanism that sets the supply line in an interruptedcondition when a temperature of the load reaches a first set temperatureand second interrupting mechanism that sets the supply line in theinterrupted condition such that the supply line cannot be returned to anenergized condition when the temperature of the load reaches a secondset temperature that is higher than the first set temperature.

Embodiments and advantages of this invention will be described in detailbelow with reference to the attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a configuration of a vehicle air-conditioningdevice to which a vehicle safety device according to an embodiment ofthis invention is applied.

FIG. 2 is a circuit diagram of a vehicle safety device according to afirst embodiment of this invention.

FIG. 3 is a sectional view showing a first bimetal switch in anenergized condition.

FIG. 4 is a sectional view showing a warm water tank of the vehicleair-conditioning device.

FIG. 5 is a perspective view of an electric heater.

FIG. 6 is a plan view illustrating an arrangement of the first bimetalswitch and a second bimetal switch relative to the electric heater.

FIG. 7 is a circuit diagram of a vehicle safety device according to asecond embodiment of this invention.

FIG. 8 is a circuit diagram of a vehicle safety device according to athird embodiment of this invention.

EMBODIMENTS OF THE INVENTION

Referring to FIGS. 1 to 6, a vehicle safety device 100 according to afirst embodiment of this invention will be described below.

First, referring to FIG. 1, a vehicle air-conditioning device 1 to whichthe vehicle safety device 100 is applied will be described.

The vehicle air-conditioning device 1 is an air-conditioning deviceinstalled in a hybrid electric vehicle (HEV) or an electric vehicle(EV). The vehicle air-conditioning device 1 includes an air passage 2having an air introduction port 2 a, a blower unit 3 that introduces airinto the air passage 2 through the air introduction port 2 a, a coolerunit 4 that cools and dehumidifies the air flowing through the airpassage 2, and a heater unit 5 that warms the air flowing through theair passage 2.

Air suctioned through the air introduction port 2 a flows through theair passage 2. Outside air from the exterior of a vehicle cabin andinside air from the interior of the vehicle cabin is suctioned into theair passage 2. The air passing through the air passage 2 is led into thevehicle cabin.

The blower unit 3 includes a blower 3 a serving as an air blowing devicethat blows air into the air passage 2 by rotating about an axial center.The blower unit 3 includes an intake door (not shown) for opening andclosing an outside air intake port through which outside air from theexterior of the vehicle cabin is taken in and an inside air intake portthrough which inside air from the interior of the vehicle cabin is takenin. By opening and closing the outside air intake port and the insideair intake port or adjusting respective openings thereof, the blowerunit 3 can adjust suctioned amounts of outside air from the exterior ofthe vehicle cabin and inside air from the interior of the vehicle cabin.

The cooler unit 4 includes a refrigerant circulating circuit 4 a throughwhich a cooling refrigerant circulates, an electric compressor 4 b thatis driven by an electric motor (not shown) to compress the refrigerant,a condenser 4 c that condenses the refrigerant compressed by theelectric compressor 4 b by discharging heat from the refrigerant to theoutside, a pressure reducing valve 4 d that expands the condensedrefrigerant in order to reduce a temperature thereof, and an evaporator4 e that cools the air flowing through the air passage 2 using therefrigerant that has been expanded so as to decrease in temperature.

The heater unit 5 includes a refrigerant circulating circuit 5 a throughwhich a refrigerant circulates, an electric pump 5 b that is driven byan electric motor (not shown) to circulate the refrigerant, an airextraction tank 5 c that removes air from the circulating refrigerant,an electric heater 5 d that warms the circulating refrigerant, a warmwater tank 6 through which the refrigerant warmed by the electric heater5 d flows, a heater core 5 e that warms the air flowing through the airpassage 2 using the refrigerant warmed by the electric heater 5 d, and amix door 5 f that adjusts flow rates of air led to the heater core 5 eand air bypassing the heater core 5 e, from among the air flowingthrough the air passage 2.

In the vehicle air-conditioning device 1, the air introduced into theair passage 2 through the air introduction port 2 a is first led intothe cooler unit 4 by the blower 3 a. In the cooler unit 4, the airflowing through the air passage 2 is cooled and dehumidified throughheat exchange with the evaporator 4 e.

The air that passes through the evaporator 4 e is divided by the mixdoor 5 f into the air that is led to the heater core 5 e and the airthat bypasses the heater core 5 e. The air led to the heater core 5 e iswarmed through heat exchange with the heater core 5 e. The air warmed bythe heater core 5 e and the air bypassing the heater core 5 e thenre-converge so as to be led into the vehicle cabin. Thus, the vehicleair-conditioning device 1 adjusts the temperature and humidity of theair introduced into the air passage 2 through the air introduction port2 a, and then leads the air into the vehicle cabin.

Next, referring to FIGS. 2 and 3, the vehicle safety device 100 and anelectric circuit 10 to which the vehicle safety device 100 is appliedwill be described.

As shown in FIG. 2, the electric circuit 10 includes a direct currentpower supply 11 serving as a power supply, and the electric heater 5 d,which serves as a load that is operated by a current supplied from thedirect current power supply 11. The electric circuit 10 also includes awater temperature sensor 23 that detects a temperature of therefrigerant in the warm water tank 6, and a controller 25 that controlsthe current supply to the electric heater 5 d on the basis of therefrigerant temperature detected by the water temperature sensor 23.

The direct current power supply 11 is a high current battery installedin a hybrid electric vehicle, an electric vehicle, or the like. Anoutput voltage of the direct current power supply 11 is a high voltageof at least 30V, and is set here at 350V. The current from the directcurrent power supply 11 is supplied to the electric heater 5 d via asupply line 12. An alternating current power supply may be used insteadof the direct current power supply 11 as the power supply.

The direct current power supply 11 also supplies a current to theelectric compressor 4 b, which serves as a different load to theelectric heater 5 d. In this case, the current supplied to the electriccompressor 4 b bifurcates from the supply line 12 downstream of a powerfuse 31, to be described below.

The electric heater 5 d is a sheath heater or a positive temperaturecoefficient (PTC) heater that generates heat when energized. In terms ofcost, the electric heater 5 d is preferably a sheath heater. Theelectric heater 5 d is housed in the warm water tank 6 in order to heatthe refrigerant used in the heating apparatus of the vehicle.

The water temperature sensor 23 is housed in the warm water tank 6. Thewater temperature sensor 23 transmits an electric signal correspondingto the detected refrigerant temperature to the controller 25.

When the temperature of the refrigerant is lower than an appropriatetemperature range, the controller 25 issues a command to a driver 20 ato apply a control current to an IGBT 20, to be described below, so thata current is supplied to the electric heater 5 d. When the temperatureof the refrigerant is higher than the appropriate temperature range, onthe other hand, the controller 25 issues a command to the driver 20 a tointerrupt the control current to the IGBT 20 so that a current is notsupplied to the electric heater 5 d. In so doing, the controller 25adjusts the temperature of the refrigerant to a desired temperature.

The vehicle safety device 100 is capable of interrupting the currentsupplied to the electric heater 5 d from the direct current power supply11 via the supply line 12 when the temperature of the electric heater 5d itself or the temperature of the refrigerant in the warm water tank 6rises above an allowable temperature range.

It should be noted that respective “set temperatures” to be describedbelow refer to “the temperature of the electric heater 5 d itself or thetemperature of the electric heater 5 d when the refrigerant in the warmwater tank 6 rises above the allowable temperature range”, and do notrefer to target temperatures during a normal warming operation.

The vehicle safety device 100 includes the insulated gate bipolartransistor (IGBT) 20 as a transistor provided on the supply line 12, abimetal switch (a first bimetal switch) 22 that switches a controlcurrent for controlling the IGBT 20, and a power supply device 24 thatsupplies the control current (DC 12V) to the IGBT 20.

Further, the vehicle safety device 100 includes a short-circuit line 30capable of short-circuiting the supply line 12 upstream and downstreamof the electric heater 5 d, the power fuse 31, which is provided on thesupply line 12 between the direct current power supply 11 and theshort-circuit line 30, and a bimetal switch (a second bimetal switch) 32provided on the short-circuit line 30.

The IGBT 20 interrupts the current supplied to the electric heater 5 dwhen the control current is interrupted, and supplies the current to theelectric heater 5 d when the control current is applied. The IGBT 20 isprovided on the supply line 12 closer to the electric heater 5 d than ashort-circuit position of the short-circuit line 30. When theshort-circuit line 30 is short-circuited, the current from the directcurrent power supply 11 does not flow to the IGBT 20. As a result, theIGBT 20 is protected from a large current generated when theshort-circuit line 30 is short-circuited.

The IGBT 20 is provided in a pair upstream and downstream of theelectric heater 5 d. More specifically, in a flow direction of thecurrent on the supply line 12, one IGBT 20 is provided downstream of acontact with one end 30 a of the short-circuit line 30 and upstream ofthe electric heater 5 d, and the other IGBT 20 is provided downstream ofthe electric heater 5 d and upstream of a contact with another end 30 bof the short-circuit line 30.

The IGBTs 20 allow the current to flow along the supply line 12 when thecontrol current is applied. When, on the other hand, the controller 25issues a command to the driver 20 a on the basis of the electric signalfrom the water temperature sensor 23 to interrupt the control currentfrom the power supply device 24, or when the control current isinterrupted by the bimetal switch 22, the IGBTs 20 stop functioning sothat the current flow along the supply line 12 is interrupted.

The bimetal switch 22 is a normally closed type switch that is normallyswitched to an energized condition. The bimetal switch 22 is a lowcurrent side bimetal switch that passes a smaller current than thebimetal switch 32 when switched to the energized condition. The bimetalswitch 22 contacts the electric heater 5 d to be capable of heattransfer. The bimetal switch 22 interrupts the control current when thetemperature of the electric heater 5 d reaches a first set temperature,and applies the control current when the temperature of the electricheater 5 d falls to a third set temperature, which is lower than thefirst set temperature. The bimetal switch 22 is provided in a pairinterposed between the power supply device 24 and the respective IGBTs20.

The first set temperature is set at a higher temperature than an upperlimit of the allowable temperature range of the refrigerant in the warmwater tank 6. Therefore, when the IGBTs 20 are controlled normally bythe controller 25, the bimetal switch 22 is maintained in the energizedcondition. The third set temperature, meanwhile, is set at a temperatureobtained when the temperature of the refrigerant in the warm water tank6 has decreased sufficiently following interruption of the controlcurrent by the bimetal switch 22. For example, the third set temperatureis set at a lower limit of the allowable temperature range of therefrigerant in the warm water tank 6.

As shown in FIG. 3, the bimetal switch 22 includes a disc-shaped bimetal22 a that deforms upon reaching a critical temperature, a pin 26 thatmoves in an axial direction when the bimetal 22 a deforms, a fixedcontact 27 a fixed within a casing, a movable contact 27 b biased towardthe fixed contact 27 a by a biasing force of a spring 28, and a pair ofterminals 29 connected respectively to the fixed contact 27 a and themovable contact 27 b. The bimetal switch 22 is switched between an opencondition, in which the current flow is interrupted, and the energizedcondition, in which the current flow is permitted, in accordance withthe deformation of the bimetal 22 a.

Heat generated by the electric heater 5 d is transmitted to the bimetal22 a either directly or indirectly. The bimetal 22 a projects downward(as shown in FIG. 3) when at a lower temperature than the criticaltemperature, and deforms so as to project upward upon reaching thecritical temperature. The critical temperature of the bimetal 22 acorresponds to the first set temperature.

When the bimetal 22 a reaches the critical temperature, therebydeforming so as to project upward, the movable contact 27 b biased bythe spring 28 separates from the fixed contact 27 a, and as a result, anon-energized condition is established. Accordingly, the bimetal switch22 is switched to the open condition such that the control currentsupplied to the IGBT 20 is interrupted.

As shown in FIG. 2, in the flow direction of the current on the supplyline 12, one end 30 a of the short-circuit line 30 is connecteddownstream of the power fuse 31 and upstream of the electric heater 5 d,while the other end 30 b is connected downstream of the electric heater5 d and upstream of the direct current power supply 11. Theshort-circuit line 30 is a conductor having an extremely smallresistance, which connects the one end 30 a and the other end 30 bconnected to the supply line 12. In other words, when the short-circuitline 30 short-circuits the upstream and downstream sides of the electricheater 5 d, the resistance of the short-circuit line 30 is smaller thana resistance of the electric heater 5 d.

The bimetal switch 32 is a normally open type switch that is normallyswitched to an open condition. The bimetal switch 32 is a high currentside bimetal switch that passes a larger current than the bimetal switch22 when switched to an energized condition. The bimetal switch 32contacts the electric heater 5 d to be capable of heat transfer. Thebimetal switch 32 has a similar specific configuration to the bimetalswitch 22, and therefore description thereof will be omitted here.

The bimetal switch 32 is switched to the energized condition when thetemperature of the electric heater 5 d reaches a second set temperature,which is higher than the first set temperature. When the temperature ofthe electric heater 5 d is lower than the second set temperature, theshort-circuit line 30 is not short-circuited. The short-circuit line 30is short-circuited when the temperature of the electric heater 5 dreaches the second set temperature such that the bimetal switch 32 isswitched to the energized condition.

The second set temperature is a critical temperature of a bimetal of thebimetal switch 32. The second set temperature is set at a highertemperature than a maximum temperature of the electric heater 5 d, whichis generated when the temperature of the electric heater 5 d increasesdue to overshoot after reaching the first set temperature such that thebimetal switch 22 interrupts the control current supplied to the IGBT 20and an interrupted condition is established on the supply line 12.Hence, when the bimetal switch 22 and the IGBT 20 are operatingnormally, the temperature of the electric heater 5 d does not reach thesecond set temperature.

The power fuse 31 is disconnected by a large current (an overcurrent)that flows momentarily when the short-circuit line 30 isshort-circuited. The resistance of the short-circuit line 30 isextremely small, and therefore, when the short-circuit line 30 isshort-circuited, a large current (an overcurrent) that is larger thanthe current flowing to the electric heater 5 d prior to short-circuitingof the short-circuit line 30 flows to the power fuse 31. The power fuse31 is disconnected by the current supplied from the direct current powersupply 11 before heat generated by a harness (not shown) for supplyingthe current exceeds an allowable temperature. The allowable temperatureis set at a temperature at which constituent components of the harnessare not damaged.

The power fuse 31 is shared by the electric heater 5 d and the electriccompressor 4 b, both of which are supplied with a current from thedirect current power supply 11. Therefore, when the power fuse 31 isdisconnected, current supply is stopped not only to the electric heater5 d but also to the electric compressor 4 b.

Next, referring to FIGS. 4 to 6, an arrangement of the bimetal switch 22and the bimetal switch 32 will be described.

As shown in FIG. 4, the warm water tank 6 includes a supply passage 6 athrough which the refrigerant is supplied, an exhaust passage 6 bthrough which the refrigerant heated by the electric heater 5 d isdischarged, and a holding member 7 that holds the electric heater 5 d inits interior. The refrigerant flowing through the warm water tank 6 iscooling water such as antifreeze, for example. The bimetal switch 22 andthe bimetal switch 32 are attached to the warm water tank 6.

As shown in FIG. 5, the electric heater 5 d includes a plurality ofparallel heat generation portions 51, and terminal portions 54 formed ateither end, to which power is supplied. The electric heater 5 d isformed in a spiral shape wound such that the heat generation portions 51are adjacent to each other in sequence. The electric heater 5 d does notnecessarily have to take a spiral shape as long as the heat generationportions 51 are adjacent to each other.

The heat generation portion 51 is formed to have an annularcross-section. Here, the cross-section of the heat generation portion 51is circular. The heat generation portion 51 includes a rectilinearportion 53 formed in a straight line, and a curved portion 52 linking anend portion of the rectilinear portion 53 to an adjacent rectilinearportion 53.

As shown in FIG. 4, the bimetal switch 22 and the bimetal switch 32 areattached to an upper portion of the warm water tank 6 so as to sandwichthe heat generation portions 51 of the electric heater 5 d together withthe holding member 7. The bimetal switch 22 and the bimetal switch 32are inserted into the interior of the warm water tank 6 from theoutside, and fastened to the outside of the warm water tank 6 by bolts.The bimetal switch 22 and the bimetal switch 32 are pressed against theelectric heater 5 d by a fastening force of the bolts.

The bimetal switch 22 is attached in a position closer to the exhaustpassage 6 b than the bimetal switch 32. The bimetal switch 32, on theother hand, is attached in a position closer to the supply passage 6 athan the bimetal switch 22.

When the refrigerant supplied to the warm water tank 6 is in thevicinity of the supply passage 6 a, the refrigerant has not yet beenwarmed by the electric heater 5 d and is therefore comparatively low intemperature. In the vicinity of the exhaust passage 6 b, the refrigeranthas been warmed by the electric heater 5 d and is thereforecomparatively high in temperature. The temperature of the electricheater 5 d itself is likewise higher in the vicinity of the exhaustpassage 6 b than in the vicinity of the supply passage 6 a. Thus, heatfrom a first part of the electric heater 5 d having a comparatively hightemperature is transmitted to the bimetal switch 22, while heat from asecond part of the electric heater 5 d having a lower temperature thanthe first part is transmitted to the bimetal switch 32.

Hence, the low current side bimetal switch 22 is switched before thehigh current side bimetal switch 32. Accordingly, the bimetal switch 22can be switched to an interrupted condition such that the controlcurrent supplied to the IGBT 20 is interrupted before the bimetal switch32 is switched to the energized condition such that the power fuse 31 isdisconnected. As a result, a safety circuit that enables the supply line12 to be returned to the energized condition can be operated before asafety circuit that makes returning to the energized conditionimpossible.

It should be noted that an amount of heat captured by the refrigerantfrom the electric heater 5 d decreases as a flow speed of therefrigerant through the warm water tank 6 decreases, and as a result,the temperature of the electric heater 5 d itself becomes more likely toincrease. On the other hand, the amount of heat captured by therefrigerant from the electric heater 5 d increases as the flow speed ofthe refrigerant through the warm water tank 6 increases, and as aresult, the temperature of the electric heater 5 d itself becomes morelikely to decrease. Hence, when bringing the bimetal switches 22, 32into contact with the electric heater 5 d, the bimetal switch 22 may bedisposed in a part of the warm water tank 6 where the flow speed of therefrigerant is low, and the bimetal switch 32 may be disposed in a partwhere the refrigerant flow speed is relatively high in comparison withthe part where the bimetal switch 22 is disposed. By disposing thebimetal switches 22, 32 in this manner, a similar effect to thatdescribed above is obtained.

Incidentally, in this embodiment, the refrigerant flow speed is lower inthe vicinity of the exhaust passage 6 b than in the vicinity of thesupply passage 6 a. Therefore, the bimetal switch 22 is disposed in thepart of the warm water tank 6 where the refrigerant flow speed is low,while the bimetal switch 32 is disposed in the part where therefrigerant flow speed is high in comparison with the part where thebimetal switch 22 is disposed.

Next, referring mainly to FIG. 2, an operation of the vehicle safetydevice 100 will be described.

In a normal condition where the temperature of the refrigerant in thewarm water tank 6 is within the allowable temperature range, the bimetalswitch 32 is maintained in the open condition such that the current flowto the short-circuit line 30 is interrupted. Further, the bimetal switch22 is maintained in the energized condition such that the controlcurrent is applied to the IGBT 20. As a result, the current from thedirect current power supply 11 is supplied to the electric heater 5 dsuch that the electric heater 5 d generates heat by which therefrigerant flowing through the warm water tank 6 is heated.

When, in this condition, the temperature of the electric heater 5 ditself or the temperature of the refrigerant in the warm water tank 6rises beyond the allowable temperature range, the vehicle safety device100 is activated. In the vehicle safety device 100, first to thirdsafety circuits to be described below are activated in three stages tointerrupt the current supplied to the electric heater 5 d from thedirect current power supply 11.

First, when the temperature of the refrigerant in the warm water tank 6rises beyond the allowable temperature range, an electric signalcorresponding to the temperature of the refrigerant is transmitted fromthe water temperature sensor 23 to the controller 25. On the basis ofthe electric signal, the controller 25 issues a command to the driver 20a not to apply the control current to the IGBT 20. As a result, thecurrent flow along the supply line 12 is interrupted. This operationcorresponds to the first safety circuit.

Here, when a flow rate of the refrigerant in the warm water tank 6decreases due to an abnormality, for example, the electric heater 5 denters a so-called empty heating condition. In this condition, thetemperature of the electric heater 5 d itself may rise above theallowable temperature range before the refrigerant temperature detectedby the water temperature sensor 23 increases.

When the temperature of the electric heater 5 d increases so as to reachthe first set temperature, the bimetal switch 22 is switched from theenergized condition to the open condition. Accordingly, the controlcurrent supplied to the IGBT 20 is interrupted regardless of the controlperformed by the controller 25, and as a result, the current flow alongthe supply line 12 is interrupted. This operation corresponds to asecond safety circuit.

When the temperature of the electric heater 5 d falls thereafter so asto reach the third set temperature, the bimetal switch 22 is switchedfrom the open condition to the energized condition. As a result, thecontrol current is applied to the IGBT 20 such that the supply line 12is returned to the energized condition.

Therefore, when the temperature of the electric heater 5 d reaches thefirst set temperature, the bimetal switch 22 interrupts the controlcurrent applied to the IGBT 20 such that the supply line 12, along whicha current is supplied from the direct current power supply 11 to theelectric heater 5 d, enters an interrupted condition. Then, when thetemperature of the electric heater 5 d falls to the third settemperature, which is lower than the first set temperature, the bimetalswitch 22 applies the control current to the IGBT 20 such that thesupply line 12 is returned to the energized condition from theinterrupted condition. Hence, in a case where the flow rate of therefrigerant through the warm water tank 6 decreases temporarily and thenreturns to normal, for example, the electric heater 5 d can be usedagain to heat the refrigerant.

It should be noted that in the vehicle safety device 100, two each ofthe IGBT 20 and the bimetal switch 22 are provided. Therefore, in thesecond safety circuit, even when one bimetal switch 22 cannot beswitched to the open condition due to an abnormality, the other bimetalswitch 22 can be switched to the open condition to compensate. In otherwords, the second safety circuit is a twofold safety circuit.

At this time, the critical temperatures of the respective bimetalswitches 22 may be dissimilated by employing as one of the bimetalswitches 22 a switch that is switched to the open condition at a highertemperature than the temperature at which the other bimetal switch 22 isswitched to the open condition, for example.

As described above, the bimetal switches 22 are normally closed typeswitches, but instead, normally open type bimetal switches that applythe control current when the temperature of the electric heater 5 dreaches the first set temperature and interrupt the control current whenthe temperature of the electric heater 5 d falls to the third settemperature may be used. In this case, IGBTs that interrupt the currentsupplied to the electric heater 5 d when the control current is appliedand supply the current to the electric heater 5 d when the controlcurrent is interrupted are used instead of the IGBTs 20.

Furthermore, when the temperature of the electric heater 5 d increasesbeyond the first set temperature due to an abnormality such that neitherof the two bimetal switches 22 can be switched to the open condition, orwhen the bimetal switches 22 are switched to the open condition but theIGBTs 20 do not interrupt the current on the supply line 12, the bimetalswitch 32 provided on the short-circuit line 30 is activated.

More specifically, when the temperature of the electric heater 5 dreaches the second set temperature, the bimetal is deformed by thetemperature of the electric heater 5 d such that the bimetal switch 32is switched to the energized condition. Accordingly, the short-circuitline 30 is short-circuited such that a large current generated by theshort-circuit flows to the power fuse 31 provided on the supply line 12.In other words, when the temperature of the electric heater 5 d reachesthe second set temperature, an overcurrent is caused to flow to thepower fuse 31 intentionally. As a result, the power fuse 31 isdisconnected, whereby the current on the supply line 12 is interrupted.This operation corresponds to the third safety circuit.

Hence, when the temperature of the electric heater 5 d rises furtherfrom the first set temperature so as to reach the second settemperature, the bimetal switch 32 short-circuits the short-circuit line30, thereby causing an overcurrent to flow such that the power fuse 31is disconnected, and as a result, the current flowing along the supplyline 12 is interrupted in such a manner that the supply line 12 cannotbe returned to the energized condition.

By disconnecting the power fuse 31, therefore, the current from thedirect current power supply 11 can be interrupted reliably even when anabnormality occurs in the IGBT 20, even if, such that the current fromthe direct current power supply 11 cannot be interrupted. As a result,the reliability with which the current supplied to the electric heater 5d from the direct current power supply 11 is interrupted can beimproved.

Further, the current flowing along the supply line 12 from the directcurrent power supply 11 bifurcates downstream of the power fuse 31 andupstream of the IGBT 20 such that a current is also supplied to theelectric compressor 4 b. In this case, the power fuse 31 is notdisconnected when the electric heater 5 d and the electric compressor 4b are operating normally. The power fuse 31 is disconnected when theshort-circuit line 30 is short-circuited by the bimetal switch 32 or anovercurrent flows through the entire circuit due to an abnormality suchas a short-circuit in the electric compressor 4 b.

By sharing the power fuse 31 among a plurality of loads in this manner,costs can be suppressed in comparison with a case where a power fuse isprovided for each load. It should be noted that a power fuse provided ina fuse box of the vehicle may be used as the power fuse 31.

Furthermore, in this embodiment, power interruption by the bimetalswitch 22 and the IGBT 20 occurs before power interruption by thebimetal switch 32 and the power fuse 31. Hence, at the point where powerinterruption by the bimetal switch 22 and the IGBT 20 occurs, power isstill being supplied to the electric compressor 4 b, and thereforefunctions of the cooler unit 4 can be maintained. For example,dehumidification and warming can be performed using preheat from thepower-interrupted electric heater 5 d while operating the cooler unit 4.Alternatively, cooling can be performed using the cooler unit 4.

The bimetal switch 22 and the bimetal switch 32 are switched to theenergized condition mechanically on the basis of the temperature of theelectric heater 5 d. Hence, a control device for short-circuiting theshort-circuit line 30 is not required, and therefore costs can besuppressed. Moreover, in comparison with a case in which a controldevice is used, operational reliability is improved.

According to the first embodiment described above, following effects areobtained.

When the temperature of the electric heater 5 d reaches the first settemperature, the bimetal switch 22 interrupts the control currentapplied to the IGBT 20, thereby establishing an interrupted condition inthe supply line 12 along which a current is supplied from the directcurrent power supply 11 to the electric heater 5 d. When the temperatureof the electric heater 5 d then falls to the third set temperature,which is lower than the first set temperature, the bimetal switch 22applies the control current to the IGBT 20 such that the supply line 12is returned to the energized condition from the interrupted condition.Hence, in a case where the flow rate of the refrigerant through the warmwater tank 6 decreases temporarily and then returns to normal, forexample, warming can be resumed using the electric heater 5 d.

Moreover, when the temperature of the electric heater 5 d rises furtherso as to reach the second set temperature, which is higher than thefirst set temperature, the bimetal switch 32 short-circuits theshort-circuit line 30, thereby causing an overcurrent to flow such thatthe power fuse 31 is disconnected, and as a result, the current flowingalong the supply line 12 is interrupted in such a manner that the supplyline 12 cannot be returned to the energized condition.

By disconnecting the power fuse 31 in this manner, the current from thedirect current power supply 11 can be interrupted reliably even when anabnormality occurs in the IGBT 20, even if, such that the current fromthe direct current power supply 11 cannot be interrupted. As a result,the reliability with which the current supplied to the electric heater 5d from the direct current power supply 11 is interrupted can beimproved.

Referring to FIG. 7, a vehicle safety device 20 according to a secondembodiment of this invention will be described below. It should be notedthat in each of the following embodiments, similar configurations tothose of the first embodiment have been allocated identical referencesymbols, and where appropriate, duplicate description thereof has beenomitted.

The second embodiment differs from the first embodiment in that a powersupply device 221 capable of controlling the control current applied tothe IGBT 20 is provided in place of the driver 20 a that adjusts thecontrol current applied to the IGBT 20.

The power supply device 221 includes a direct current power supply 224that supplies the control current (DC 12V) to the IGBT 20, thecontroller 25 that controls the flow of the control current, and anamplifier 226 that adjusts the control current on the basis of a commandfrom the controller 25.

In the vehicle safety device 200, when the temperature of therefrigerant in the warm water tank 6 increases beyond the allowabletemperature range, an electric signal corresponding to the temperatureof the refrigerant is transmitted from the water temperature sensor 23to the controller 25 via the amplifier 226. On the basis of the electricsignal, the controller 25 issues a command via the amplifier 226 not toapply the control current to the IGBT 20. As a result, the current flowalong the supply line 12 is interrupted.

Further, when the temperature of the electric heater 5 d rises to thefirst set temperature, the bimetal switch 22 is switched from theenergized condition to the open condition. Accordingly, the controlcurrent applied to the IGBT 20 is interrupted regardless of the controlperformed by the controller 25 via the amplifier 226, and as a result,the current flow along the supply line 12 is interrupted.

In the second embodiment described above, similarly to the firstembodiment, when the temperature of the electric heater 5 d reaches thefirst set temperature, the IGBT 20 and the bimetal switch 22 set thesupply line 12 along which the current supplied to the electric) heater5 d from the direct current power supply 11 flows in the interruptedcondition. When the temperature of the electric heater 5 d then falls tothe third set temperature, which is lower than the first settemperature, the IGBT 20 and the bimetal switch 22 return the supplyline 12 to the energized condition from the interrupted condition.

Moreover, when the temperature of the electric heater 5 d rises furtherso as to reach the second set temperature, which is higher than thefirst set temperature, the bimetal switch 32 is switched to theenergized condition such that the power fuse 31 is disconnected, and asa result, the current flowing along the supply line 12 is interruptedsuch that the supply line 12 cannot be returned to the energizedcondition. Therefore, the reliability of current interruption when anabnormality occurs in the electric heater 5 d can be improved.

Referring to FIG. 8, a vehicle safety device 300 according to a thirdembodiment of this invention will be described below. Similarly to thefirst embodiment, although not shown in FIG. 8, the direct current powersupply 11 also supplies a current to the electric compressor 4 b servingas a different load to the electric heater 5 d. In this case, thecurrent supplied to the electric compressor 4 b bifurcates from thesupply line 12 between the power fuse 31 and the IGBT 20.

The third embodiment differs from the respective embodiments describedabove in that a temperature fuse 322 is used in place of the bimetalswitch 22 to interrupt the control current applied to the IGBT 20.

The vehicle safety device 300 includes the temperature fuse 322, whichis disconnected when the temperature of the electric heater 5 dincreases.

The temperature fuse 322 is provided in a pair interposed between theamplifier 226 of the power supply device 221 and the respective IGBTs20. The temperature fuse 322 is switched when the temperature of theelectric heater 5 d rises to the first set temperature.

In the vehicle safety device 300, when the temperature of therefrigerant in the warm water tank 6 increases beyond the allowabletemperature range, an electric signal corresponding to the temperatureof the refrigerant is transmitted from the water temperature sensor 23to the controller 25 via the amplifier 226. On the basis of the electricsignal, the controller 25 issues a command via the amplifier 226 not toapply the control current to the IGBT 20. As a result, the current flowalong the supply line 12 is interrupted.

Further, when the temperature of the electric heater 5 d rises to thefirst set temperature, the temperature fuse 322 is disconnected by thetemperature of the electric heater 5 d. Accordingly, the control currentapplied to the IGBT 20 is interrupted regardless of the controlperformed by the controller 25, and as a result, the current flowingalong the supply line 12 is interrupted such that the supply line 12cannot be returned to the energized condition.

Furthermore, when an abnormality occurs such that the temperature of theelectric heater 5 d increases beyond the first set temperature butneither of the two temperature fuses 322 can be disconnected, thebimetal switch 32 provided on the short-circuit line 30 is activated.

More specifically, when the temperature of the electric heater 5 dreaches the second set temperature, the bimetal is deformed by thetemperature of the electric heater 5 d such that the bimetal switch 32is switched to the energized condition. Accordingly, the short-circuitline 30 is short-circuited such that a large current generated by theshort-circuit flows to the power fuse 31 provided on the supply line 12.In other words, when the temperature of the electric heater 5 d reachesthe second set temperature, an overcurrent is caused to flow to thepower fuse 31 intentionally. As a result, the power fuse 31 isdisconnected, whereby the current on the supply line 12 is interrupted.

Hence, when the temperature of the electric heater 5 d rises furtherfrom the first set temperature so as to reach the second settemperature, the bimetal switch 32 short-circuits the short-circuit line30, thereby causing an overcurrent to flow such that the power fuse 31is disconnected, and as a result, the current flowing along the supplyline 12 is interrupted such that the supply line 12 cannot be returnedto the energized condition.

By disconnecting the power fuse 31, therefore, the current from thedirect current power supply 11 can be interrupted reliably even when anabnormality occurs in the IGBT 20, even if, such that the current fromthe direct current power supply 11 cannot be interrupted. As a result,the reliability with which the current supplied to the electric heater 5d from the direct current power supply 11 is interrupted can beimproved.

In the third embodiment described above, when the temperature of theelectric heater 5 d reaches the first set temperature, the temperaturefuse 322 is disconnected, whereby the IGBT 20 cuts off the supply line12 along which the current supplied to the electric heater 5 d from thedirect current power supply 11 flows such that the supply line 12 cannotbe returned to the energized condition.

When the temperature of the electric heater 5 d rises further so as toreach the second set temperature, which is higher than the first settemperature, the bimetal switch 32 is switched to the energizedcondition such that the power fuse 31 is disconnected, and as a result,the current flowing along the supply line 12 is interrupted such thatthe supply line 12 cannot be returned to the energized condition. Thus,the reliability of current interruption when an abnormality occurs inthe electric heater 5 d can be improved.

Embodiments of this invention were described above, but the aboveembodiments are merely examples of applications of this invention, andthe technical scope of this invention is not limited to the specificconstitutions of the above embodiments.

For example, in the above embodiments, the temperature of the electricheater 5 d is detected as the load, but instead, the temperature ofanother device such as an electric motor may be detected. Likewise inthis case, the vehicle safety devices 100, 200, and 300 can interruptthe current from the direct current power supply 11 reliably when anabnormality occurs.

This application claims priority based on Japanese Patent ApplicationNo. 2012-100929 filed with the Japan Patent Office on Apr. 26, 2012, andJapanese Patent Application No. 2012-281693 filed with the Japan PatentOffice on Dec. 25, 2012, the entire contents of which are incorporatedinto this specification.

The embodiments of this invention in which an exclusive property orprivilege is claimed are defined as follows:

What is claimed is:
 1. A vehicle safety device installed in a hybridelectric vehicle or an electric vehicle to be capable of interrupting acurrent supplied from a power supply to a load via a supply line,comprising: a first interrupting mechanism adapted to set the supplyline in an interrupted condition when a temperature of the load reachesa first set temperature; and a second interrupting mechanism adapted toset the supply line in the interrupted condition such that the supplyline cannot be returned to an energized condition when the temperatureof the load reaches a second set temperature that is higher than thefirst set temperature.
 2. The vehicle safety device as defined in claim1, wherein the first interrupting mechanism returns the supply line tothe energized condition when the temperature of the load decreases to athird set temperature that is lower than the first set temperature. 3.The vehicle safety device as defined in claim 2, wherein the firstinterrupting mechanism comprises: a transistor provided on the supplyline to interrupt the current supplied to the load when a controlcurrent thereof is interrupted or applied; and a switching mechanismadapted to switch between interruption and application of the controlcurrent in accordance with the temperature of the load.
 4. The vehiclesafety device as defined in claim 3, wherein the switching mechanisminterrupts the control current when the temperature of the load reachesthe first set temperature and applies the control current when thetemperature of the load decreases to the third set temperature, and thetransistor interrupts the current supplied to the load when the controlcurrent is interrupted and applies the current supplied to the load whenthe control current is applied.
 5. The vehicle safety device as definedin claim 3, wherein the switching mechanism applies the control currentwhen the temperature of the load reaches the first set temperature andinterrupts the control current when the temperature of the loaddecreases to the third set temperature, and the transistor interruptsthe current supplied to the load when the control current is applied andapplies the current supplied to the load when the control current isinterrupted.
 6. The vehicle safety device as defined in claim 3, whereinthe switching mechanism is a first bimetal switch to which heat from afirst part of the load is transmitted, the second interrupting mechanismis second bimetal switch to which heat from a second part of the load istransmitted, and the second part of the load has a lower temperaturethan the first part.
 7. The vehicle safety device as defined in claim 6,wherein the second interrupting mechanism comprises: a short-circuitline on which the second bimetal switch is provided and which is capableof short-circuiting the supply line upstream and downstream of the load;and a power fuse provided on the supply line between the power supplyand the short-circuit line, and the second bimetal switch short-circuitsthe short-circuit line when the temperature of the load reaches thesecond set temperature.
 8. The vehicle safety device as defined in claim5, wherein a current that bifurcates from the supply line downstream ofthe power fuse is supplied from the power supply to an other load thatis different to the load, and the power fuse is shared by the load andthe other load.
 9. The vehicle safety device as defined in claim 8,wherein the load is an electric heater used in a vehicleair-conditioning device, and the other load is an electric compressorused in the vehicle air-conditioning device.
 10. The vehicle safetydevice as defined in claim 1, wherein the second set temperature is setat a higher temperature than a maximum temperature of the load, which isgenerated when the temperature of the load increases due to overshootafter reaching the first set temperature such that the firstinterrupting mechanism sets the supply line in the interruptedcondition.
 11. The vehicle safety device as defined in claim 2, whereinthe first interrupting mechanism comprises: a transistor provided on thesupply line to interrupt the current supplied to the load when a controlcurrent thereof is interrupted and apply the current supplied to theload when the control current is applied; and a first bimetal switchthat contacts the load to be capable of heat transfer, interrupts thecontrol current when the temperature of the load reaches the first settemperature, and applies the control current when the temperature of theload reaches the third set temperature that is lower than the first settemperature, and the second interrupting mechanism comprises: ashort-circuit line capable of short-circuiting the supply line upstreamand downstream of the load; a second bimetal switch that is provided onthe short-circuit line, contacts the load to be capable of heattransfer, and short-circuits the short-circuit line when the temperatureof the load reaches the second set temperature that is higher than thefirst set temperature; and a power fuse provided on the supply linebetween the power supply and the short-circuit line.
 12. The vehiclesafety device as defined in claim 2, wherein the first interruptingmechanism comprises: a transistor provided on the supply line to applythe current supplied to the load when a control current thereof isinterrupted and interrupt the current supplied to the load when thecontrol current is applied; and a first bimetal switch that contacts theload to be capable of heat transfer, applies the control current whenthe temperature of the load reaches the first set temperature, andinterrupts the control current when the temperature of the load reachesthe third set temperature that is lower than the first set temperature,and the second interrupting mechanism comprises: a short-circuit linecapable of short-circuiting the supply line upstream and downstream ofthe load; a second bimetal switch that is provided on the short-circuitline, contacts the load to be capable of heat transfer, andshort-circuits the short-circuit line when the temperature of the loadreaches the second set temperature that is higher than the first settemperature; and a power fuse provided on the supply line between thepower supply and the short-circuit line.
 13. A vehicle safety deviceinstalled in a hybrid electric vehicle or an electric vehicle to becapable of interrupting a current supplied from a power supply to a loadvia a supply line, comprising: first interrupting means for setting thesupply line in an interrupted condition when a temperature of the loadreaches a first set temperature; and second interrupting means forsetting the supply line in the interrupted condition such that thesupply line cannot be returned to an energized condition when thetemperature of the load reaches a second set temperature that is higherthan the first set temperature.